Surface-emitting semiconductor lasers that emit radiation in the direction perpendicular to the substrate are of considerable interest in view of wide range of their potential applications. There have been several approaches (vertical resonators, second-order grating coupling, and inclined mirrors) to achieve lasing through the surface. Among these, vertical-cavity surface- emitting lasers have the benefit of planar geometry and stable single- longitudinal-mode oscillation. Small-area low-threshold-current lasers can be used in optical computing and can be integrated with other optoelectronic devices to form part of monolithic optoelectronic integrated circuits and optical interconnects. Their low-divergence circular output beam simplifies the optics requirements and facilitates coupling into optical fibers. Vertical-cavity surface-emitting lasers can also be easily arranged in one- or two-dimensional arrays to form high-power sources which could find applications in free-space optical communication and as solid-state laser pumps.